title: Second-harmonic generation in GFP-like proteins.
abstract: The second-order nonlinear optical properties of green fluorescent proteins (GFPs), such as the photoswitchable Dronpa and enhanced GFP (EGFP), have been studied at both the theoretical and experimental levels. In the case of Dronpa, both approaches are consistent in showing the rather counterintuitive result of a larger second-order nonlinear polarizability (or first hyperpolarizability, beta) for the protonated state, which has a higher transition energy, than for the deprotonated, fluorescent state with its absorption at lower energy. Moreover, the value of beta for the protonated form of Dronpa is among the highest reported for proteins. In addition to the pH dependence, we have found a wavelength dependence in the beta values. These properties are essential for the practical use of Dronpa or other GFP-like fluorescent proteins as second-order nonlinear fluorophores for symmetry-sensitive nonlinear microscopy imaging and as nonlinear optical sensors for electrophysiological processes. An accurate value of the first hyperpolarizability is also essential for any qualitative analysis of the nonlinear images.
authors.affiliation: Department of Chemistry and Institute for Nanoscale Physics and Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200D and F, B-3001 Leuven, Belgium.
authors.forename: Inge
authors.initials: I
authors.lastname: Asselberghs
authors.forename: Cristina
authors.initials: C
authors.lastname: Flors
authors.forename: Lara
authors.initials: L
authors.lastname: Ferrighi
authors.forename: Edith
authors.initials: E
authors.lastname: Botek
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.forename: Hideaki
authors.initials: H
authors.lastname: Mizuno
authors.forename: Ryoko
authors.initials: R
authors.lastname: Ando
authors.forename: Atsushi
authors.initials: A
authors.lastname: Miyawaki
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Mark
authors.initials: M
authors.lastname: Van der Auweraer
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
mesh_terms: D049452:Green Fluorescent Proteins / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure
chemical_list: D049452:Green Fluorescent Proteins